Underground storage of liquefied gases



Sept. 14, 1965 M. F- VAN HORN UNDERGROUND STORAGE OF LIQUEFIED GASES 4 Sheets-Sheet 1 Filed Jan. 16, 1962 COMPRESSOR CONDENSER 62 LIQUID SALES INITIAL PUPIGE VAPOR LIQUID INVENTOR Sept. 14, 1965 M. F. VAN HORN 3,205,665

UNDERGROUND STORAGE OF LIQUEFIED GASES Filed Jan. 16, 1962 4 Sheets-Sheet 2 INVENTOR. MORSE F VAN HORN Z ZSMJA a;

Sept. 14, 1965 M. F. VAN HORN 3,205,665

UNDERGROUND STORAGE OF LIQUEFIED GASES Filed Jan. 16, 1962 4 Sheets-Sheet 3 INVENTOR. MORSE F MW HORN fie. 4

Sept. 14, 1965 M. F. VAN HORN UNDERGROUND STORAGE OF LIQUEFIED GASES Filed Jan. 16, 1962 4 Sheets-Sheet 4 INVENTOR. MORSE F VAN Hare/v BY a United States Patent This invention relates to the underground storage of liquefied gases and to the construction and preparation of underground facilities for such storage.

The fluids that may be stored by this invention are normally in the gaseous state at temperatures above the freezing point of water and at atmospheric pressures, but are liquefied when subjected to pressures substantially higher than atmospheric at temperatures considerably below those normally encountered in the temperate areas of the world. Examples of such fluids are ammonia, nitrogen, hydrogen, oxygen, argon, methane, ethane, propane, and butane. There are many others. Some are highly flammable, so that their storage always entails special precautions; all are difficult to store in large quantities.

Above-ground storage consumes considerable power in keeping the gases liquefied or expensive structures to hold the gases under pressure, especially when large quantities are involved.

Underground storage of liquefied gases has heretofore relied on natural caverns or on existing or specially constructed wells, all quite deep in the ground. Such facilities are diflicult to find and very expensive to construct. Moreover, the prevention of the seepage of vapor or liquid through the earth has been a problem. Attempts have been made to rely on the natural imporosity of some rock formations or on the freezing of interstitial water to prevent seepage, but there have often been passages through the rocks relied on, and the interstitial water has not sealed everywhere, as where there have been dry porous pockets of earth or rocks.

An important object of this invention is to provide a system for the underground storage of liquefied gases that is cheaper to construct and operate, safer, and more practical than the systems heretofore in use.

The present invention does not rely on interstitial water or on imporous rocks to seal the walls, although such water may be frozen where it is present as part of the sealing system, and imporous rocks are always helpful. However, the invention is not limited to environments having sufficient interstitial underground water or special rock formations. The invention can be used in many different types of substrata.

Another object of the invention is to provide underground storage facilities by means of simple construction methods, and a further object is to provide a simple yet efiicient system of maintaining operation.

Broadly speaking, the invention comprises excavating a desired site to provide an open pit, providing a roof for the lower part of the pit, sprinkling the side walls of the pit, below the roof with water until there is a continuous film of water covering the walls, providing a mud slurry around the edges and over the top of the roof, and using the liquefied gases to freeze the water on the walls so as to prevent leakage through the Walls, and also to freeze the mud slurry mix and thereby seal the edges of the roof. A lake of water is then provided on top of the roof to prevent the pressure inside the cavern from lifting the roof "ice or otherwise causing escape of the contained gas. A recirculation and condensation system enables maintenance of the desired temperature-pressure conditions, while the lake and the earth and bedrock in which the pit lies provide insulation that hold the power consumption of the recirculation system to a minimum.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment.

In the drawings:

FIG. 1 is a phantom-like view in perspective and partly in section of an underground storage facility embodying the principles of the invention, just prior to putting the facility into operation.

FIG. 2 is a fragmentary view in perspective of a portion of the area where the roof rests on a shoulder of the pit.

FIG. 3 is an enlarged view in end elevation and in section of the facility of FIG. 1 after excavation and at the beginning of operations, when water is being sprayed on the walls. Some portions are broken to conserve space.

FIG. 4 is a view similar to FIG. 3 showing the device in operation at a later stage when the sealing Water is being frozen.

P16. 5 is a view similar to FIGS. 3 and 4 showing the device at a still later stage, when the gas is being introduced in liquefied form for storage thereof.

As shown in the drawings, the invention contemplates the excavation of a steep-sided underground pit or silo 10, the size being determined by the structural characteristics of the rock or soil in which the excavation is carried on and by the desired capacity of the storage facility. For example, about 1,600,000 gallons of liquefied gas may be stored in an underground silo 10 about forty feed Wide by one hundred feet long by about fifty feet deep. The silo 16 preferably has quite steep walls 11 in bedrock with a shoulder 12 at the top of the walls 11 and well below the ground level 13. Above the silo 10 is a pit 14 with less steep walls 15 that are used to confine a man-made lake 16 of fresh water approximately forty feet deep in a completed and filled facility, the lake 16 lying above a roof 17 on the top of the storage silo 10.

Before excavating, it is wise to make test borings to determine the structural qualities of the bedrock in which the silo 10 and pit 14 will be dug, and after excavation it is wise to examine in detail the side Walls 11 and 15 to be sure of their structural quality. Also, an analysis of the ground water or interstitial water, if any, is desirable in order to make sure that it is not so salty that it has an abnormally low freezing temperature. A supply of fine earth, possibly from the excavation, is provided near by, for use in making the mud slurry, to be described later.

Upon finishing the excavation work, the roof 17 is placed over the top of the silo 10, bearing upon the bedrock shoulder 12 on each side. This roof or cover 17 may be arched like a Quonset but with rods 18 extending across it at suitable intervals, or steel truss work may be employed. The roof 17 may be galvanized iron, aluminum, or other suitable material. The internal pressure of the stored gas will be countered by the pressure of the lake 16, so that the roof 17 does not have to be able to hold this pressure by its own strength. Moreover, a strong arch of frozen mud 19 will aid in providing the needed strength. The roof 17 is itself preferably covered by an imperforate film 20 of plastic, either a sprayed-on coating, or a laid-on sheet, to provide a thin sealing layer that helps to prevent escape of gas at a later stage. The roof 17 is then preferably covered by about one or two inches of lightweight aggregate material 21 of a type having a high insulating factor, such as expanded Perlite, vermiculite, or diatomaceous earth.

Far above the roof 17, and above the surface of the lake 16 is a control bridge 22, which may span the lake 16 and which supports a piping system and some control instruments. From the bridge 22, a pipe 23 descends through the roof 17 to a sprinkler system 24 installed in the interior of the silo 10, with nozzles 25 located where liquid sprayed from them can cover all the interior surface of the roof 17 and cover all the area of the side walls 11 of the silo 10. An additional pipe 26 descends from the bridge to nozzles 27 that can be used to sprinkle water gently over the entire top of the storage silo roof 17, or the mud over it, so that the water can cover the mud over the entire roof. A water supply pipe 28 leads to the pipe 26 through an olf-on valve 29 and to the pipe 23 through an off-on valve 30. A flow control valve 29a is also in the pipe 28 to enable control of the sprinkling rate. A gas-supply pipe 31 also leads to the pipe 23 through an off-on valve 32. If desired, the gas pipe 31 may lead to a separate interior sprinkler system duplicating substantially the system 24, but the use of a single system is often more economical.

From the bridge 22 a casing 33 descends through the roof 17 to a low point 34 at the bottom of the silo 10, and in the casing 33 is an interior pipe 35 having a deepwell pump 36 near the lower end for pumping liquid (water or gas) out of the silo 10. A valve 37 connects the upper end of the pipe 35 to a liquid sales outlet pipe 38, by which liquefied gas is Withdrawn from storage for sale. Preferably, a valve 39 connects the pipe 38 to a recycle pipe 40 that is supported by the bridge 22 and leads down through the roof 17 to a lower end 41. The recycle pipe 40 preferably has a valve 42 on the bridge 22 and a valve 43 connecting it to the casing 33. A vent pipe 44 extends up from an inlet 45 in the upper part of the roof 17 to three valves: a flare valve 46, a safety relief valve 47, and a recycle valve 48. The valve 48 leads back to the pipe 40 through a cycling system 60 comprising a suitable compressor, evaporator, condenser arrangement that compresses vented gas and cools it to the desired temperature. The line 40 is also connected to the line 31 for incoming liquid gas by a line 49 and suitable valves.

The roof 17 has a removable cover 50 over a hole 51 enabling, during the construction and pipe installation phases, an inspection sling 52 to be suspended from the bridge 22 by a cable .53 for inspection of the cavern or silo 10.

Temperature gauges 55 and pressure gauges 56 are installed at critical points in the silo 10, preferably in duplicate at each point, to lessen the risk from defects or breakage, and at several points in the roof 17. Preferably, they are located in the bottom of each corner and halfway up and at the top of the wall. A control panel 57 of recording instruments, connected to the thermometers 55 and pressure indicators '56 (the lines connecting them being broken or omitted to avoid obscuring the meaning of the drawing), is installed on the bridge 22. A liquid-level indicator 58, preferably of the magnetic float type, may also be installed in or beside the casing 33 and at any other desired location.

The construction of the silo 10 having been completed along with all piping and facilities, the cavern sprinkling system 24 is inspected by a man suspended in the sling 52 to make sure that all walls 11 of the silo 10 and the inside walls of the roof 17 are going to be covered with water when water is put into the pipe 23. With everything in order, the sprinkler system 24 can be used to wet down the interior walls 11 of the silo 10. For this purpose, the valves 29 and 30 are opened to send water from the supply pipe 28 down through the pipe 23 to the sprinkler nozzles 25 and 27. Both the water used for sprinkling and that in the lake 16 are preferably as pure as is feasible (i.e., salt free) so that the freezing temperature will be approximately 32 F., in order to avoid unnecessary consumption of power when freezing it or in keeping it frozen during the actual storage of gas. As soon as the entire interior walls of the silo 10 are wet down, the valve 30 is closed.

This water sprinkling is followed by purging the lines 23, 24 of water by a dry gas from a line 59, if the same sprinkler system is to be used with gas, and, if an inflammable gas is to be stored in this facility, the silo 10 is also purged of air, by sending dry inert gas such as carbon dioxide through the pipes 31 and 23 to the nozzles 25,, the air going out the vent pipe 44 through the flare valve 46. (The air purge could, of course, if desired, precede the water sprinkling.) This prevents the flammable gas from forming an explosive or inflammable mixture when it is put in later. Excess water may be pumped out by the pump 36.

Once the silo 10 is properly purged, the liquefied gas to be stored can be injected into the silo 10 in its liquid state from the pipe 31 and valve 32 into the purged pipe 23 and thence to the nozzles 25. The flare valve 46 is opened, and the initial portion of this mixture of storage and inert gas is flared, as a safety measure and to avoid mixing the purging gas or air with the stream going through the cycling unit 60. As soon as a check indicates that nearly pure vapor of the liquid gas being injected is being flared, the valve 46 is closed or pinched down, the valve 48 is opened, and a compressor 61 in the cycle unit 60 is set in operation. As soon as the compressor 61, with the other elements such as an evaporator and condenser 62, of the cycle unit 60, begin to operate, the valve 42 is opened, enabling the liquid gas to return .to the silo 10 through the line 40. Later, the valve 43 may also be opened to send gas also into the casing 33. Liquid gas is still, during this period, being injected through the sprinkler system 24 into the interior of the silo 10.

A large exit area is provided at each of the nozzles 25; so the initial injection of the liquefied gas escapes rapidly into the silo 10, vaporizing and dropping the temperature, thereby causing the water on the walls 11 and on both sides of the roof 17 to freeze. The refrigerating action of the gas vaporized inside the silo 10 almost immediately freezes the water covering the walls 11 and the roof interior drawing heat from the surrounding silo walls 11 and roof 17. The cold penetrates out into the bedrock, gradually cooling a larger and larger area. As the silo 10 is filled and stands a while, eventually a somewhat greater area will be cooled, providing a cold barrier in the area around the walls, to keep the silo 10 cold for a crust distance suflicient to prevent leaking at the pressures involved.

Meanwhile, the deck sprinklers 26 operate slowly to keep the entire top of the roof 17 and the mud 19 over it wet down, as well as the edges of the silo 10. The

sprinklers 26 may be operated continuously or inter-v mittently. While this is going on, a fine, light soil is placed on top of the roof 17. The water makes this into a. slurry of mud 19 which is frozen as it covers the roof 17. This mud 19 serves as a sealant around the edge of the roof 17 where it rests on the shoulder 12, and, as later water is added, provides a frozen mixture that is heavier than water. It does not, as ice would, float up to the top of the lake 16, but maintains a sealing layer at the bottom of the lake 16 and over the roof 17. It also helps to act as a support for the water, because this frozen rnud 19 has considerable strength.

Temperatures and pressures are important at this stage of the operation. For example, for propane it will be minus 44 F. and for ammonia minus 28 F. The pressures at point 56 is not allowed to exceed two inches of water column during this initial filling and freezing operation. The recording thermometers 55 and pressure gauges 56 at various points in the installations are watched very closely during this period. As the temperatures in the silo continue to drop lower, the frozen slurry 19 covering the entire top of the silo 10 is frozen quite solid. If desired, additional soil may be added and more water sprinkled in order to increase the thickness of the cap. When the roof 17 has become covered with about four inches of solid frozen slurry 19, the pressure in the silo 10 may be raised gradually up to one pound gauge. At this time the entire shoulder 12 outside the roof 17 is covered with a shallow frozen lake of mud slurry 19.

Any openings in the silo which might permit escape of the gas are readily perceived by the escaping gas forming bubbles coming up through the mud slurry 19 and water surrounding the top of the deck. In the event that there is any indication of leaking from the silo 10, the following procedure is followed: the line 31 is purged by dry gas from the line 59. After purging, water is then reinjected through the sprinkler system 24 by opening the valve 30, once again wetting down the interior Walls of the silo 10. Meanwhile, of course, the entire top of the silo 10 is wet down or covered with an ice cap. This water is injected at a rapid rate under a pressure preferably exceeding 100 pounds per square inch and freezes almost immediately upon contact with the walls 11 and top 17 of the cavern. Water is then re-purged from the lines as before, by dry gas and the liquid gas sent in again through the sprinkler system 24, insuring freezing of the injected water. This also eifectively seals off any leaks in top, side walls or bottom of the silo which might have developed subsequent to the initial sprinkling and injection of the gas. The re-injection is an important advantage of the invention.

With the cycling operation in operation, pressure can now be permitted to come up to about minus 1 p.s.i. gauge, and it can then be determined whether the silo 10 is completely sealed by the frozen applied water and interstitial water. If the seal is good enough, the silo 10 can be filled. Gas continues to come through the line 40, the valve 42, and to the outlet 41, as well as through the line 31 through the sprinkler system 24, the pressure still being maintained at minus 1 lb. per square inch. As the frozen cap 1Q continues to increase in thickness on the deck or roof 17 of the silo 10, additional screened top soil is added and the sprinkler 26 is kept going very slowly. This Wet slurry 19 is kept frozen from the internal temperature of the silo. As the slurry becomes frozen to a depth of approximately 6 inches, the sprinkler rate is increased on top of the roof 17, and the lake 16 begins to fill.

The valve 29 may now be opened wide, enabling addi tional water to go through the sprinkler system 26 on top of the roof 17 and to fill that reservoir or lake 16 which surrounds the entire installation. The water placed over the roof 17 into the man-made lake 16 above the silo 10 provides a hydrostatic head that is balanced against the pressure exerted by the gas stored within the silo 10. As the lake 16 is deepened, ,more fine earth is added to help to maintain the frozen mud slurry 19 with its specific gravity above that of water, all to avoid the floating of the arch of mud-ice oif the roof 17. As the silo 10 continues in operation, the arch of frozen mud 19 gradually thickens and acts as a supporting medium for containing the contents and pressure of the cavern and as a support for the water over the roof. As the water depth in that reservoir or lake 16 increases, for each foot of depth the interior pressure in the silo 10 is permitted to rise one-half pound gauge. The thickness of the mud-ice cap 19 on the top of the cavern is continually checked and as it freezes thicker, additional screened earth is added to the middle of the top of the deck.

While the water level on the lake 16 is raised rather rapidly, at the same time the pressure in the cavern is also raised, at the same rate of one-half pound per additional foot of lake water thereon until the maximum depth of the lake, e.g., about forty feet, is realized. At this time the pressure in the interior of the silo 10 is about twenty pounds gauge and the pressure on the roof 17 is offset by the weight of the forty-foot-deep lake. When the silo 10 reaches its operating temperature, somewhere in the range of 0 F. to 10 F., there is a thick arch of frozen mud slurry 19 covering the entire roof 17 of the silo 10, with a depth of water 16 on the outside or edge of the roof 17 which is increased gradually as the operating temperatures and pressures are reached. The mudice 19 surrounding the silo at all points is impermeable to gases and is a strong supporting medium. If at some future time it is desired to evacuate the contents of the silo 10, the water is drained from the lake 16 while the gas pressure is reduced in the silo; in practical application this is a reversal of the filling process.

With the silo in operation, and in lieu of bringing the product or cycle unit liquid back through the valve 42 and the pipe 40, the valve 43 is opened and the valve 42 is closed, sending the liquid gas through the annulus of the 12-inch casing 33. In order to remove the product from the cavern, the pump motor 36 is placed in operation, and the liquid is pumped through the line 38 to liquid sales. At this time, the valve 43 is closed and the valve 39 is opened enabling the product from production or from the liquid cycle unit to enter the liquid sales line 38, along with that gas being evacuated through the line 33 through the line 38, by action of the pump 36. The advantage of bringing the cycle unit or production liquid gas through the valve 43 and through the annulus of the tubing would lie in the fact that this warm gas re-entering keep free of any ice or condensate that might have formed around the bottom of that tubing where the pump 36 installed at or near the bottom of the silo 10.

This invention is not limited to a silo 10 shaped in that form as shown in the enclosed sketches. Almost any shape of silo or cavern, man-made or natural, can be utilized for this type of storage, prerequisites being:

(1) The practical limitations on the installation of sprinkling systems to cover the entire interior, top, side walls, and bottom of the existing cavern, mined or natural.

(2) The practical limitations on a slope to a low point in the cavern, which will provide for the installation of a pump with gravity flow of a liquid gas to the pump for removal from the cavern. This point is important, in that drainage should come to one point for evacuation of the liquid, or drifts be driven to permit drainage to one point, or, if it were a large cavern and economics justifies it, the possibility of the installation of several pumps at low points might be considered. For example, 2. Worked out coal mine can be used. A complete survey of this area is made determining grades of floors and the problems in sealing the portals, which can be done by installation of concrete blocking with slurry fill between; then concrete walls are poured with a slurry pumped in between these two walls in each portal, effectively sealing portals against escape of the gas. Sprinkler systems are installed where they wet down the entire inside of the mine. The procedure would then be very similar to that previously described: the wetting down through the sprinkling system, the injection of the gas through the sprinkling system with, of course, a close check on pressures and temperatures during this process. A survey is made for location of the evacuation pump and site located for drilling a hole from the surface to the low point in the cavern. The pump is installed as described and when cavern is sheathed with ice on the inside and pressure test had proven it was impermeable, liquid from the cycling unit or from production is injected through the annulus of the tubing and when it was decided to remove the liquid gas therefrom, it is pumped out through the tubing installed inside the casing; and shipped by pipe line or other means of transportation to areas of utilization.

To those skilled in the art to which this invention re lates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A method for providing an underground gas storage facility in bedrock and the like, comprising excavating a pit in said bed rock to provide a lower portion and an upper portion,

covering said lower portion to provide a closed chamber,

sprinkling water on the interior surfaces of said chamher so that it covers said surfaces with an inner lining of water, and

sprinkling liquefied gas on said interior surfaces, thereby freezing the water thereon to provide a continuous sealing layer of ice lining the inside of said chamber and preventing gas seepage through said bed rock.

2. The method of claim 1, wherein a mud slurry is provided over the top of said lower portion and is frozen by the gas in said lower portion, to seal the top of said lower portion.

3. A method for storing gas underground, comprising excavating a pit in bed rock to provide a lower portion and an upper portion meeting at a ledge, covering said lower portion, from ledge to ledge, to

provide a closed chamber,

sprinkling water on the interior surfaces of said chamber to cover the surface of the bed rock with a film of water, adding a mud slurry over the top of said chamber, injecting liquefied gas under pressure on said interior surfaces of said chamber, thereby freezing the water and the mud slurry, the frozen Water providing a lining preventing gas seepage into said bed rock, and

adding liquefied gas to be stored into said chamber while adding water over said frozen mud slurry in amounts sufficient to balance the gas pressure in said chamber by the pressure of water over said frozen mud slurry.

4. A method for storing gas underground, comprising excavating a pit to provide a lower silo portion in bed rock and an upper portion above said silo, meeting it at a ledge,

covering said silo, from ledge to ledge, to provide a closed chamber,

sprinkling water on the interior surfaces of said silo chamber to provide a water film covering the bed rock,

adding a mud slurry over said silo,

injecting liquefied gas under pressure on said interior surfaces of said silo chamber, thereby freezing the water and the mud slurry, the frozen water then providing an ice lining preventing gas seepage into said bed rock,

testing said chamber forleaks, and, when leaks are found,

again sprinkling water on said interior surfaces, and

again injecting said liquefied gas under pressure thereon to freeze said added water, and then adding liquefied gas to be stored into said silo while adding water over said mud slurry to balance the gas pressure in said silo chamber by the pressure of water over the covering.

5. A method for providing underground gas-storage facilities, comprising excavating a pit going down into bed rock to provide a steep-sided lower portion and an upper portion meeting at a ledge, providing a sprinkling system in said lower portion, roofing said lower portion from ledge to ledge to provide a silo therebeneath, sending water through said sprinkling system to coat the interior surfaces of said silo with water,

covering said roofing with a mud slurry, purging the sprinkling system of water, and sending liquefied gas through said sprinkling system to I impinge against said interior surfaces of said silo and freeze the water on said surfaces to provide an ice lining on the surface of the bed rock preventing gas seepage into the bed rock and to freeze the mud slurry. 6. A method for storing gas underground, comprising excavating a pit to provide a steep-sided lower portion and an upper portion meeting at a ledge, providing a sprinkling system in said lower portion, roofing said lower portion from ledge to ledge to provide a silo therebeneath, sending water through said sprinkling system to coat the, interior surfaces of said silo with water, covering said roofing with a mud slurry, purging the silo of air and the sprinkling system of Water, sending liquefied gas through said sprinkling system to impinge upon said interior surfaces of said silo and freeze the water on said surfaces and to freeze the mud slurry, and adding liquefied gas to said silo while adding water over said frozen mud slurry in an amount sutficient to balance the gas pressure in said silo with the pressure of water over the frozen mud slurry. 7. A method for storing gas underground, comprising excavating a pit to provide a steep-sided lower portion and an upper portion meeting at a ledge, providing a sprinkling system in said lower portion, roofing said lower portion from ledge to ledge to provide a silo therebeneath, sending water through said sprinkling system to coat the interior surfaces of said silo with water, covering said roofing with a mud slurry, sending dry gas through said sprinkling system to purge the silo of air and the sprinkling system of water, sending liquefied gas of the type to be stored through said sprinkling system to impinge on said interior surfaces of said silo and freeze the water on said surfaces and to freeze the mud slurry, checking for leaks from said silo, and, if leaks are found, sending dry gas again through said sprinkling system to purge said liquefied gas therefrom, sending water again through said sprinkling system to add additional water coating to said interior surfaces, once more sending dry gas through said sprinkling system to purge the water therefrom, again sending liquefied gas through said sprinkling system to freeze the added water, and adding liquefied gas to said silo while adding water over said frozen mud slurry to balance the gas pressure in said silo with the pressure of water over the frozen mud slurry. 8. An underground storage facility for liquefied gases, including in combination:

a deep pit having a lower silo portion in bedrock and an upper portion joined at a shoulder, a roof supported on said shoulder, a coating of water icecompletely covering the surfaces of the walls of'the lower portion to prevent seepage of gas into the bedrock and covering the interior of the roof, and means to put liquefied gas in and to remove it from said silo portion, and

a covering on said roof for balancing the pressure of the gas against said roof.

9. The facility of claim 8 having a coating of frozen mud slurry covering said roof and sealing its edges to said shoulder.

10. The facility of claim 9 having a water lake over said mud slurry balancing the pressure of the gas against said roof.

11. An underground storage facility for liquefied gases, including in combination:

a deep pit having a lower steep-sided silo portion and an upper somewhat less steep-sided portion joined at a ledge,

a roof supported on said ledge,

a coating of water ice covering the walls of the silo portion and the interior of the roof,

a coating of frozen mud slurry covering said roof and sealing its edges to said ledge, and providing a strong supporting structure;

means to put liquefied gas in, to remove it from, and

to recirculate some of it to, said silo, and

a water lake over said frozen mud slurry balancing the pressure of the gas in said silo against said roof.

12. An underground storage facility for liquefied gases, including in combination:

a deep pit having a lower steep-sided silo portion and an upper somewhat less steep-sided portion joined at a shoulder,

a roof supported on said shoulder,

a first sprinkling system inside said silo able to cover the entire walls of said silo and the interior of said roof,

a second sprinkling system above said roof able to cover the exterior surface of said roof,

means to send water into each said sprinkling system,

means for purging water from said first sprinkling system,

means for purging air from said silo,

means for sending liquefied gas into said first sprinkling system after purging thereof, to freeze the previously introduced water so as to provide a coating of ice on said walls and roof,

means for adding dirt on the top of the roof so that the water added over said roof forms a mud slurry frozen when liquefied gas is sent through said first sprinkling system and a water lake over said roof balancing the pressure of the gas against said roof.

13. An underground storage facility for liquefied gases,

including in combination:

a deep pit having a lower steep-sided silo portion and an upper somewhat less steep-sided portion joined at a shoulder,

a thin metal roof supported on said shoulder,

a plastic covering over said roof sealing it against leaks,

a first sprinkling system inside said silo able to cover the entire walls of said silo and the interior of said roof,

:1 second sprinkling system above said roof able to cover the exterior surface of said roof,

means to send water into each said sprinkling system,

means for purging water from said first sprinkling system,

means for purging air from said silo,

means for sending liquefied gas into said first sprinkling system after purging, to freeze the previously introduced water and to provide a coating of ice on said walls and roof,

means for adding dirt on the top of the plastic covering, so that water through said sprinkling system forms a mud slurry frozen by the cool temperature of said roof, said frozen mud slurry providing strong physical support, and

a water lake over said frozen mud slurry balancing the pressure of the gas against said roof.

14. The facility of claim 13 having additional means for adding liquefied gas at ascertained pressures to said silo and for reliquefying and recirculating vaporized gas from said silo.

15. A method for storing gas underground, comprismg excavating a pit to provide a steep-sided lower portion and an upper portion meeting at a ledge,

providing a sprinkling system in said lower portion,

roofing said lower portion from ledge to ledge to provide a silo therebeneath,

sending water through said sprinkling system to coat the interior surfaces of said silo with water,

purging the silo of air and the sprinkling system of water,

sending liquefied gas through said sprinkling system to impinge upon said interior surfaces of said silo and freeze the water on said surfaces, and

adding liquefied gas to said silo while filling over said roofing in an amount sutficient to balance the gas pressure in said silo with the pressure on top of the roofing.

16. A method for storing gas underground, comprisexcavating a pit to provide a steep-sided lower portion and an upper portion meeting at a ledge,

providing a sprinkling system in said lower portion,

roofing said lower portion from ledge to ledge to provide a silo therebeneath,

sending water through said sprinkling system to coat the interior surfaces of said silo with water,

sending dry gas through said sprinkling system to purge the silo of air and the sprinkling system of water,

sending liquefied gas of the type to be stored through said sprinkling system to impinge on said interior surfaces of said silo and freeze the water on said surfaces,

checking for leaks from said silo, and if leaks are found,

sending dry gas again through said sprinkling system to purge said liquefied gas therefrom,

sending water again through said sprinkling system to add additional water coating to said interior surfaces,

once more sending dry gas through said sprinkling system to purge the water therefrom,

again sending liquefied gas through said sprinkling system to freeze the added water, and

adding liquefied gas to said silo While adding material over said roofing to balance the gas pressure in said silo.

17. An underground storage facility for liquefied gases,

including in combination:

a deep pit having a lower steep-sided silo portion in bed rock and an upper somewhat less steep-sided portion joined at a ledge,

a roof supported on said ledge,

a coating of water ice covering the surfaces of the Walls of the silo portion and the interior of the roof and preventing seepage of gas into the bed rock,

means to put liquefied gas in, to remove it from, and

to recirculate some of it to, said silo, and

material over said roof balancing the pressure of the gas in said silo against said roof.

18. An underground storage facility for liquefied gases,

including in combination:

a deep pit having a lower steep-sided silo portion going down into bed rock and an upper somewhat less steepsided portion joined at a shoulder,

a roof supported on said shoulder,

a sprinkling system inside said silo able to cover the entire walls of said silo and the interior of said roof,

means to send water into said sprinkling system,

means for purging water from said sprinkling system, means for purging air from said silo,

means for sending liquefied gas into said sprinkling systern after purging thereof, to freeze the previously introduced water so as to provide a coating of ice on the surfaces of said walls and roof, said coating preventing seepage of gas into said bed rock,

means for adding material on the top 'of the roof so that the pressure of the gas against said roof is balanced.

References Cited by the Examiner UNITED STATES PATENTS 2,301,780 11/42 Heinzelman 62235 FOREIGN PATENTS 6/61 Pakistan.

EARL J. WITMER, Primary Examiner. JACOB SHAPIRO, Examiner. 

1. A METHOD FOR PROVIDING AN UNDERGROUND GAS STORAGE FACILITY IN BEDROCK AND THE LIKE, COMPRISING EXCAVATING A PIT IN SAID BED ROCK TO PROVIDE A LOWER PROTION AND AN UPPER PORTION, COVERING SAID LOWER PORTION TO PROVIDE A CLOSED CHAMVER, SPRINKLING WATER ON THE INTERIOR SURFACES OF SAID CHAMBER SO THAT IT COVERS SAID SURFACES WITH AN INNER LINING OF WATER, AND SPRINKLING LIQUEFIED GAS ON SAID INTERIOR SURFACES, THEREBY FREEZING THE WATER THEREON TO PROVIDE A CONTINUOUS SEALING LAYER OF ICE LINING THE INSIDE OF SAID CHAMBER AND PREVENTING GAS SEEPAGE THROUGH SAID BED ROCK. 